The present invention relates to a method of separating solid particles from suspensions in a centrifuge, as well as to a centrifuge for such a separation. More particularly, it relates to a method and a centrifuge in which a solid-liquid mixture is separated by a combination of sedimentation and filtration with the aid of a centrifugal force.
There are basically two different groups of centrifuges namely solid-jacket centrifuges and filter centrifuges. In the solid-jacket centrifuges, the heavy phase sediments on a drum wall, whereas the lighter phase flows out via a weir. These centrifuges are used for example for clarifying liquids. In the filter centrifuges, the liquid flows through a filter cake and a filter means and subsequently into the separating chamber. These centrifuges are used mainly for dewatering of mud. The special feature of the inventive centrifuge is that both a filtration and a sedimentation take place in the same. Such a clarifying filtering centrifuge cannot be associated with the known centrifugal action.
U.S. Pat. No. 3,389,855 discloses a centrifuge for materials difficult to filter. The separation which is performed here by superposing of two different separation processes. The separation of a suspension into a liquid and a solid phase is carried out by sedimentation and filtration. This centrifuge substantially includes two advantageously parallel plate-shaped bodies which are fixedly connected with a rotatable shaft and extend normal to the latter and which form a hollow space for receiving the liquid. This hollow space is closed at its periphery by a tubular body displaceable in direction of the rotatable shaft and can be opened for discharge of the solid material. A separating insert composed of a fabric is mounted normal to the rotatable shaft in a recess of one of the plates and serves as a filtering means. The rear wall of the chamber is provided for mounting with the front wall with several braces. The suspension flows axially through a hollow shaft directly into the hollow space and exits partially through the filtering means and partially via a deflecting disk directly through the axis-close opening. Because of the feeding of the suspension via the hollow shaft directly into the filtering chamber of the centrifuge indefinite flow conditions and a non-uniform cake formation take place.
Because of a relatively great opening of the filter means, a penetration of the filtrate is provided, i.e. the filtrate is united with the solid material. An excessively great number of pins on the rear wall of the chamber has the great disadvantage that during the rotation the pins act as a mill and because of this the solid particles in the suspension are further comminuted. The separation of small particles of emulsions is difficult. The great number of pins also causes disturbances in the flow discharge. A further disadvantage is the mounting of the filtering fabric on the flat faces of the filter plates, whereby the filtrate discharge is difficult. A predetermined residual moisture of the filter cake cannot be attained.